Fetch JSON returns the result with narrow typing

fetchJSON.js

// @ts-check

import * as fs from 'node:fs'

/** Fetches JSON returns the result with narrow typing. */
export let fetchJSON = /** @type {(input: RequestInfo | URL, init?: RequestInit) => any} */ (
	async (/** @type {string} */ input, config = any) => {
		const response = await fetch(input, config)
		const responseJSON = await response.json()

		typedHash[input] = JSON.stringify(responseJSON)

		setTyping()

		return responseJSON
	}
)

/** Path to the typing for this script. */
const typedPath = new URL('./fetchJSON.d.ts', import.meta.url)

/** Text used to populate the typing for this script. */
const typedText = `type JFetch<T> = (\n\tPromise<any>\n)\n\nexport declare function fetchJSON<T extends string>(resource: T): JFetch<T>`

/** Hashmap used to store typing results. */
const typedHash = /** @type {Record<string, string>} */ (Object.create(null))

/** Updates the typing file. */
const setTyping = () => fs.writeFileSync(typedPath, typedText.slice(0, 20) + Object.entries(typedHash).reduce(
	(list, [ input, responseJSON ]) => list + `T extends "${input}" ? Promise<${responseJSON}> :\n\t`,
	''
) + typedText.slice(20))

const any = /** @type {any} */ (null)